Carrier telegraph system



*Och 20, 1931. l v P, THORP v I 1,827,860

CARRIER TELEGRAPH SYSTEM Fild Oct. 22, 1929 2 sheets-sheen 1 ATTORNEY lOct. 20, 1931. .v P, THORP v 1,827,86

CARRIER TELEGRAPH SYSTEM.

Filed 0G13. 22. 41929 2 Sheets-Sheet 2 v I y i Sendz Iam l @21m |||I||||@Irl-ferm@ ||||l|||| MWMW Zine Carrel/Lt gaat lz etector wud# w etector@agout 57.47 INVENToR v v l mv v ATTORNEY Patented Oct. 20.- 1931UNITED; STATI-:s

PATENT VAUGHN 1. moar, oir arm mail, .mizsimnBSIGNOn 'ro .Aumont'rimaracial: im mnemnwconrm. A concussion or Naw You reuma rameursapuntan mea amber se, me. sensi iro. 491,513.

This invention relates to telegraphsystems and more articularlytoimprovements in systems uti izing kcarrier frequency currents inconnection with the transmissionv of the. i5 telegraph messages.

In the arrangements of this invention the carrier frequency current issuppressed and either one or both sidebands of the signalmodulatedcarrier are transmitted over the line. Receiving Larrangements arerovided l of this invention will provide in the system which re uirenoloca `carrier current. A system em odying the features improved signaltransmission in that it affords the equivalent of polar operation. Afurther feature of the arran ements of the invention is that the eiectofine equivalent changes on bias in signal reception will be minimized.Furthermore, an increased number of channels in the same frequency rangemay be provided with the arrangements of the invention. The arrangementsalso cause the signal to noise ratio to be increased, thus reducin interference with the signals. Further objects and features of theinvention will appear more fully from' the detailed description thereofhereinafter given. p

The invention may be more fully understood from the following'description, together with accompanyin drawin Figuresl, 2, 3, 4', 5, 6and l of whic the in vention is illustrated.v Fig. 1 is a circuitdiagramY illustratinga preferred embodiment of the invention. Figs. 2to'7inclusive, illustrate the wave shape ofthe signaling currents invarious portions of the system.

In Fig.- 1 is shown a circuit diagram of sending and receivingapparatuslocatedatone end of a carrier telegraph line. A connection may beestablished with-the carrier telegraph line by circuit 1 which isconnected to a common sending circuit 3. Connected to circuit 3 isacircuit 5 which includes a filter 6, an amplifier 7, anda frequencybridge 8. The bridge 8 is connected toa circuit 9 which Ywill include anoscillator or source of carrier-,frequency 10. 1 tionof carrier currentfrom this .source t0 circuit 9 may be controlled by the short-cir` cuit11, which in, turn is controlled by they vat the beginning and end of adot si inthe The applical sending relay 12 in the subscribers loopcircuit- 13. Alzey 14 is shown for operating the sending relay 12. Whenthe sending relay armature 1s on its spacing contact, the output of thecarrier oscillator is short-circuited.

When the armature is on its marking contact, the carrier current isallowed to flow into the frequency bridge 8. This bridge circuit isbalanced at the carrier frequenc by a resistance and a parallel tunedcircuit tuned to the carrier frequency. The neutral cuit, lbutfreuencies other than ythe carrier A fre uency w l pass through withrelatively sma l attenuation. When a si al modulat ed carrier wave isapplied to t e bridge circuit, such as occurs when the subscriberstelegraph h ey is closed, the side band frequencies will pass rthroughthe frequency bridge to the sending amplifier and filter. This willconsist of a short train of waves al. This is more clearly shown in Fig.4, w ich is labeled line current and input to detector.. Fig. 2 showsthe sending loop current and Fig. 3 showsthe carrier input to thefrequency bridge. Other carrierv channels mightV be connected .tothe-sending circuit 3 by-means of circuits such as 15. l'

Fre uencies similar to'those heretofore describe transmitted from thedistant end of the carrier line, are transmitted overcircuits 2 and' 4and thence over circuit 16 to the receiving ilter 17. They would then betrans-y mitted through amplifier 18 to the detector` 19.

vThe detector output circuit 20 is com leted over the contactsv of apolar relay 2 and thence through either of the operatin windings of the.receiving relay l23 to the attery 22.` The holding windings of thereceiving relay 23 are .connectedover the armature andy contacts ofvsaid relay to the oppositelyr poled batteries 24 and 25. The loopcircuit' I 26,.which includes the lsounder 27, is connected to thevarmature of the receiving recircuit from the receiving relay armatureto ground. In Fig. 1 the` receiving relay circuit is shown just after amarking pulse has been received and in condition to receive a spacingpulse when it comes in from the line. A holding current is passedthrough the lower windings of the receiving relay, as shown in Fig. 6,and serves to keep the receiving relay armature on the proper contactbetween ulses. Let it be assumed that the telegraph ey at. the sendingstation is opened and the carrier input to the frequency bridge issuddenly stopped. A train of waves will be again transmitted over theline and rectified at the receiving end. The rectified vcurrent passesthrough the armature and contact of relay 21 and one winding of thereceiving relay in such a direction as to cause it to overcome theeffect of the holding current and move to its spacing contact. -Afterthis has occurred, the holding current reverses and holds the armatureon the spacing contact; the auxiliary polar relay 21 connects thereceiving relay winding to the detector plate circuit in such a way thatthe next incoming pulse will operate the receiving relay armature to itsother contact. Since the above described arrangement is in eii'ect onein which the transmission of si nals is polar, a poorer wave shape may eused than if the transmission were of the open and close type. For thisreason, it would be possible to use filters having a smaller band widthand thereby obtain more channels in a iven frequency range.

If the lters are made with a sharp cut-off, it may be possible to locatethe, carrier frequency near the outer edge of .the normal band used forsignaling and thereby eliminate one of the side bands. It seems thatthis could be done readily since the frequency bridge eliminates thecarrier frequency and attenuates considerably the frequencies close toit on either side. The amount of attenuation of the lower frequencycomponents which are deemed desirable, it is understood that it iscapable of embodiment in many and other widely varied forms withoutdeparting from the spirit of the invention as eline in the appendedclaims.

What is claimed is:

1. The method of telegraph signaling which comprises modulating acarrier frequency current with telegraph signals so as to produce pulsesof current of the carrier frequency, suppressing said carrier andtransmitting sidebands of the signal-modulated carrier at the beginningand end of each pulse of current of the carrier frequency whic are alsoproduced by modulation.

2. In a carrier telegraph system the method of signaling which comprisestransmitting only the sidebands of the signal-modulated carrierfrequency current for brief intervals at the beginning and end of eachtransmitted pulse of carrier frequency current.

3. In a carrier telegraph system the method of signaling which comprisesmodulating carrier current in accordance with signals so as to producepulses of the carrier current and sidebands which occur onl at thebeginning and end of4 each pulse of the carrier current, transmittingonly the sidebandsof the signal-modulated carrier frequency current,receiving said transmitted sideband currents, rectifying said receivedsideband currents, and utilizing said rectified current to operatesignaling means.

4.. A telegraph line, sending apparatus connected thereto comprising asource of carrier frequenc current, means for interrupting currentfii'om said source in accordance with signaling currents so as to'produce sidebands at the beginning and end of each pulse of carriercurrent, a Wheatsone bridge circuit for suppressing the carriercomponent of said signal-modulated'carrier frequency current, and meansfor transmitting said sidebands of said signal-modulated carrier to saidline.

5. A telegraph line, a sending circuit connected to said line, a sourceof carrier frequency current connected to said sending circuit, meansconnected to said sending circuit for modulating the carrier currenttransmitted over said sending circuit with si aling currents so as toproduce pulses o the carrier current and sidebands which occur at thebeginning and end of each pulse of the carrier current, and a frequencybridge circuit in said sending circuit balanced at said carrierfrequency whereb said carrier frequency will be suppresse and thesideband piglmponents transmitted to said telegraph 6. A telegraph line,sending apparatus connected thereto comprising a source of carrierfrequency current, means for modulating current from said source withsignalv ing currents, means for suppressing the carrier component ofsaid signal-modulated carrier frequency current, means for transmittingthe sidebands of said signal-modulated carrier over said telegraph line,and

equal to the resistance of the anti-resonant l receiving apparatusconnected to said telegraph line comprising a detector, a receivingrelay and a polar relay, said receiving relay having operating windingsdi'erentially connected in the plate circuit of said detector over thecontacts of said polar relay, and a y circuit for said polar relaycompleted over the armature of said receiving relay.

7. A frequency bridge circuit for carriery signaling systems designed tosuppress the carrier waves after modulation, comprising an anti-resonantcircuit tuned to the frequency of the carrier waves 'and connected asone of the arms of the bridge circuit, and a resistance connected asanother of the arms of the bridge circuithaving a magnitude circuit atthe frequency of the carrier waves.

In testimony whereof, I have signed my name to this specification this21st day of October, 1929.

. VAUGHN P. THORP.

